How to conform a mesh ontop of another mesh?
I seem to have arrived at a solution thanks to the comments by @Mobin.

Place circle mesh where you want it with Snapping -> Face

Circle mesh -> Edit mode -> Select face -> I to inset and create internal geometry. A few loop cuts to improve its ability to bend.



You need to get rid of the vertices in the middle, or the geometry does strange things when applying the shrinkwrap.

Then you give the circle a shrinkwrap modifier. Modifiers -> Shrinkwrap
Set the body as the target, change the offset to the smallest amount that doesn't clip through.